A walk by Westminster Bridge to test my new 80-400mm lens with my D810 offered the usual fair of views of the London Eye, seagulls and boats on the river, until I looked at Parliament.

I took some pictures of “big ben” (actually the Queen Elizabeth Tower, the bell is known as “Big Ben”) and realised there were some people on it.

The great clock on the tower has been getting a wash from cleaners this week, who are bravely abseiling down the 314ft tower to check the four dials of the iconic timepiece.

The clock was installed in April 1859 but at first would not work as the cast-iron minute hands were too heavy. Once they were replaced by lighter copper hands, it began keeping time in May 1859.

Big Ben was last given a scrub back in 2010. The clock will continue to keep time during the cleaning process, but the hands on the face being “washed” (as water might be damaging the cleaning is done via a chemical detergent) are disconnected from the mechanism and do not move. As well as ensuring all 312 pieces of pot opal glass are sparkling clean, the workers are going to be checking the dials for damage.

Deputy keeper of the clock Steve Jaggs said: “The process is complex and requires a real head for heights. We have an expert team who will ensure that the clock is thoroughly cleaned and that this piece of our national heritage is safeguarded for future generations.”

I was unreliably informed that in the 60s this job was accomplished with dusters on bits of string…

Taken with my Nikon D810 and Nikon 80-400mm AF-S FX VR G